OK, so let me see what you think could be gained by using an SSD. 10 times faster? 100 times? Unless we are talking a couple of orders of magnitude improvement, I just see this as rearranging the deck chairs on the Titanic.
To give us an idea of where you are starting, what is the size of your II folder, at what number of entries in a given patient are you seeing significant slowness? 10 items? 50 items?
To answer your questions I'm willing to replicate your install in our environment with 15K spindles, then again on SSD just so that we have actual benchmarks.